The present invention relates to an optical apparatus such as a camera, which is so constituted as to perform a predetermined optical adjustment by guiding a lens, which is supported by a lens frame, by means of guide shafts and moving it along an optical axis by a propulsive mechanism constituted of a lead screw and a driven member (e.g., a nut) fitted on the lead screw.
In an optical apparatus such as a camera, generally, a specific optical element such as a focusing lens supported by a lens frame, is guided by a guide member such as a guide shaft and moved in an optical axis direction. The optical element is then driven in the optical axis direction by a propulsive mechanism constituted of a lead screw and a driven member (e.g., a nut) fitted on the lead screw, thereby performing a predetermined optical adjustment such as a focus adjustment.
The propulsive mechanism moves the lens frame using the lead screw as a drive source, and the driven member thereof is constituted of a nut or a half nut in order to convert a turning force of the lead screw to a moving force thereof in the optical axis direction. In the propulsive mechanism having such a constitution, if a nut member is over-driven beyond a normal range for some reason, the following trouble will be caused.
If the nut member is over-driven in a direction of the top end of the lead screw, it is likely to fall from the lead screw. On the other hand, if the nut member is over-driven in a direction of the bottom end of the lead screw, it often bites a motor shaft.
To prevent the bite of the nut member, Jpn. Pat. Appln. KOKAI Publication No. 7-43591 discloses a means for cutting a power supply to a motor to stop a nut before the nut reaches a set physical stopping position, using an electrical position sensor.
However, even though the above position sensor is used, the bite of the nut member cannot be prevented completely but there remains a possibility that a bite will occur. It is therefore likely that a great trouble will be caused without any measures against the bite.